Portable wireless communication device

ABSTRACT

A portable communication device which also has an infrared transceiver. A portable communication device can automatically establish infrared communication sessions with another portable communication device or desktop computer having an infrared transceiver. The portable communication device and the other device may exchange textual and graphical information, as well as the current time, and then reconcile the newly received information with that information in possession before the communication session began. Multiple portable communication devices and computers may communicate, while conserving battery power, using a time division multiplexing scheme where the infrared transceivers are active during a short, periodic time slots. Multiple communication session may overlap in time as long as they are not active during the same time slot.

RELATED APPLICATION

This application is a continuation of patent application Ser. No.08/149,993 filed Nov. 10, 1993 now U.S. Pat. No. 5,440,559 issued Aug.8, 1995.

FIELD OF THE INVENTION

The present invention relates to a portable wireless communicationdevice capable of establishing an infrared communication link withanother portable communication device, computer, or other electronicdevice.

RELEVANT ART

Many people use electronic devices to assist in keeping theirinformation organized. One person may use a desktop personal computer atwork and at home, a laptop or notebook computer on the road, a palmtopcomputer for those times when a notebook computer is too large, and awatch capable of holding scheduling information to ensure thatinformation is always available.

Although these devices can communicate with each other, the process isnot automatic and typically involves connecting cables. Infraredcommunication is possible, but because of its power consumption, musttypically be disabled most of the time to conserve battery power.

What is needed is an automatic, wireless communication method and devicethat simplifies the transfer of information among electronic deviceswithout requiring large amounts of battery power.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a personalcommunication device and a second device, both having respectiveinfrared transceivers communicate using their infrared transceivers. Todo so, the second device periodically transmits a hailing message usingits infrared transceiver. The personal communication device periodicallyattempts to receive a hailing message using its infrared transceiver.When the personal communication device receives a hailing message, ittransmits a response message.

As a feature, the personal communication device includes a security listof acceptable identification codes. The hailing message includes the anidentification code uniquely identifying the second device. Uponreceiving a hailing message, the personal communicating device comparesthe received identification code with the security list of acceptableidentification codes. If there is a match the personal communicationdevice transmits a response message.

As another feature, the second device includes a security list ofacceptable codes. The personal communication device also transmits anidentification code uniquely identifying it in its response message.When the second device receives the response message, it compares thereceived identification codes with its security list. Upon finding amatch, the second device then sends any information intended to be sentto the personal communication device.

As another feature, when the personal communication device receivesinformation from the second device, it sends any information intended tobe sent to the second device.

Information exchanged between the personal communication device and thesecond device may include time of day information which has anassociated code signifying the relative degree of accuracy of theinformation. This information can be used by the device receiving theinformation in resetting its internal time of day clock.

As another feature, the second device may continuously alternate betweentransmitting a hailing message and attempting to receive a responsemessage, thereby increasing the probability of initiating acommunication session with the personal communication device.

As another feature, for the synchronization of the transmit-receiveprocess, the personal communication device may include a group listcontaining at least one group name. The personal communication deviceperforms a hashing operation on a group name resulting in a time slotnumber of a time division multiplexing scheme. The personalcommunication device attempts to receive hailing messages within thetime slot.

As another feature, the personal communication device transmits ahailing message during the time slot. Each time slot may have multiplestart times; the personal communication device can be assigned a starttime by assigning it a device number.

According to another aspect of the present invention, a computer havingan infrared transceiver and a means of communicating with a broadcastfacility for transmitting wireless communications may send a message toa personal communication device having an infrared transceiver and awireless receiver according to the due date of the message. If the duedate of the message is less than a predetermined period in the futurefrom the current date, the computer communicates the message to thebroadcast facility for transmission to the wireless radio-frequencyreceiver of the personal communication device. Otherwise, if the duedate of the message is greater than a predetermined period in the futurefrom the current date, the computer transmitting the message to thepersonal communication device via the infrared transceivers.

The foregoing and additional objects, features and advantages of thepresent invention will be more readily apparent from the followingdetailed description of preferred embodiments thereof which proceed withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a personal communication device accordingto the present invention.

FIG. 2 is a schematic block diagram showing a personal communicationdevice communicating with a personal computer.

FIG. 3 is a chart showing the times during which a personalcommunication device attempts to receive hailing messages from otherdevices.

FIG. 4 is a chart showing the establishment of a communication sessionbetween a portable communication device and a personal computer.

FIG. 5 is a flow chart showing the logic performed by a portablecommunication device and a personal computer in establishing acommunication session.

FIG. 6 is a schematic block diagram showing a personal communicationdevice communicating with a personal computer on a network.

FIG. 7 is a schematic block diagram showing two personal communicationdevices communicating with each other.

FIG. 8 is a signal chart showing various establishments of communicationsessions between two personal communication devices.

FIG. 9 is a flow chart showing the logic performed by a personalcommunication device in attempting to establish a communication sessionwith another personal communication device.

FIG. 10 is a chart showing multiple time slots in a time divisionmultiplex scheme.

FIG. 11 is a chart showing multiple transmit start times within a singletime slot.

FIG. 12 is a schematic block diagram showing a personal communicationdevice having two modes of communicating with a personal computer.

FIG. 13 is a flow chart showing the logic performed by the personalcomputer of FIG. 12 is deciding which mode of communication to use forcommunicating with the personal communication device of FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, where like reference numbers refer tolike elements, and particularly to FIG. 1, a personal communicationdevice (PCD) 20 according to the present invention comprises theelements of a digital watch. Thus, the PCD includes a real-time clock 22which can be set to the current time and which will keep accurate trackof time from that point into the future. The PCD includes a display 24on which the PCD can show the time, as well as other information, as isdiscussed below. Buttons 26 on the PCD allow the user to enterinformation into the PCD, such as the current time, appointmentinformation, and alarms.

The real-time clock 22, and the display are controlled by a centralprocessing unit (CPU) 27 which accepts the inputs from the buttons 26.The CPU executes programs stored in a Read-Only Memory (ROM) 28 and usesRandom Access Memory (RAM) 30 for temporary storage of information inputby the user, as well as information received from other sources.

An infrared (IR) transceiver 32 enables the PCD 20 to communicate withother electronic devices. The IR transceiver can communicate at 192,000bits per seconds.

Optionally, the PCD 20 may also include a radio-frequency receiver, suchas a paging receiver 34. The paging receiver enables the PCD to receivemessages anywhere in a broad geographic area.

Referring now to FIG. 2, the PCD 20 is preferably contained in awristwatch form factor. Straps hold the PCD on the operator's wrist. Thedisplay 24 and buttons 26 are positioned as is conventional for digitalwatches. The infrared transceiver 32 is positioned so that its line ofsight is likely to be unobstructed by the user's sleeves.

The PCD 20 need not be strapped on its user's wrist. However, the lineof sight limitation of IR communication makes a wristwatch an ideallocation for the PCD. When contained within a wristwatch, a PCD islikely to be always worn by its user, and accessible.

A first aspect of the present invention is for a PCD 20 and a computer40 to automatically communicate and exchange information, as shown inFIG. 2. The personal computer may be the user's home computer or thecomputer assigned to the user at work.

A desktop personal computer 40 is unlikely to be battery powered andtherefore is not extremely sensitive to power consumption. The personalcomputer 40 continuously attempts to establish a communication sessionwith a PCD 20 by transmitting a "hailing" message using its IRtransceiver 42.

Preferably, the IR transceiver 42 of the desktop personal computer 40 islocated where it is in a direct line-of-sight with the PCD 20 when theuser is typing. A location directly in front of the user's hands, suchas on the keyboard or on the front of the display monitor, meets thisrequirement.

Refer now to FIG. 4, in which the upper line 60 in row (A) representsthe behavior of the personal computer 40 in attempting to establish anIR communication session with the PCD 20. The personal computeralternates between times 60 of duration T3 when it is transmitting ahailing message and times 62 of duration T4 when it is attempting toreceive a response. As shown in FIG. 4, the time periods T3 and T4 areequal, and are one millisecond each. This need not be the case; thetransmitting and receiving times need not be one millisecond and neednot be equal.

A hailing message preferably is a relatively short sequence ofinformation. For example, the hailing message of the personal computer40 may consist of the current time and location, if known. In such acase, other IR receiving devices (not shown) within range of thecomputer could use the information contained in the hailing message tokeep their internal real-time clocks synchronized with the computer'sinternal real-time clock.

Alternatively, or in addition to transmitting the current time, thehailing message may include an identification code (ID) which uniquelyidentifies the device transmitting the hailing message. This code may beused by receivers of the hailing message as an address to compare withan internal security list. If the ID is not in the security list, thereceiver will not respond to the hailing message. A PCD 20 could beconfigured to communicate with a personal computer 40 by having its IDstored in its security list.

As will be appreciated, other information can be transmitted in ahailing message. However, to decrease the amount of time the portablecommunication device must activate its infrared transceiver to receivehailing messages, preferably, the length of the hailing message islimited.

In an exemplary version of the present invention, the hailing message is192 bits, that is, 24 bytes, long. Since the IR transceivers 32, 42communicate at 192,000 bits per second, the hailing message takes 1millisecond to transmit.

The PCD 20, being the size of a wristwatch, is limited to usingsmall-volume, and thus small energy capacity, batteries. As such, it isvery sensitive to power expenditures. Its IR transceiver 32 uses arelatively significant amount of energy. For example, if the IRtransceiver uses 10 mA, and if the PCD operates on a 100 milliamp-hourbutton battery, then the PCD could activate its IR transceiver for onlyten hours before the battery would be expended. Therefore, continuousoperation of the IR transceiver would result in unacceptably shortbattery life.

According to the present invention, a PCD 20 does not continuouslyattempt to establish a communication session. To conserve battery power,the PCD 20 operates its IR transceiver 32 intermittently, and then onlylong enough to ensure that it receives any transmission from the IRtransceiver 42 of the personal computer 40.

Referring now to FIG. 3, the line 50 represents when the PCD 20 isattempting to receive a hail. When the line is in the upper position, asshown by reference number 52, the PCD is attempting to receive a hail.In the lower position, as shown by reverence numbers 54, the PCD's IRtransceiver 32 is depowered.

The time T2 between attempts to communicate is a balance betweenextending battery life and ensuring that a communication session occurswhen the PCD 20 and the personal computer 40 are within range of eachother. An exemplary time for T2 is 10 seconds.

The PCD 20 attempts to receive only long enough to ensure that itdetects the beginning portion of a transmission from a personal computer40. This minimum amount of time T1 is just longer than the time betweenconsecutive beginnings of hailing messages from the personal computer40. This is equal to T3 plus T4, and is two milliseconds in a preferredembodiment.

The PCD 20 thus powers its IR transceiver 32 for only 2 millisecondsevery 10 seconds. Using the battery capacity and power consumption ratesdiscussed above, this would result in a battery life of almost sixyears. Although other circuitry within the PCD will cause actual batterylife to be less than six years, operation of the IR transceiver 32according to the present invention results in a relatively small drainon the battery.

Referring again to FIG. 4, the lines in rows (B) and (C) represent thebehavior of the PCD in attempting to establish a communication sessionwith a personal computer 40.

As shown in row (B) of FIG. 4, the PCD 20 may attempt to receive 52'while the personal computer 40 is transmitting 64 a hailing message.Because its IR transceiver does not detect the beginning of the personalcomputer's hailing message, it must wait until the beginning of the nexthailing message 66 which begins at the time represented by the verticalline 68. Since this occurs before time period T1 elapses, the PCD isable to detect the hailing message.

Once the PCD 20 detects the beginning of a hailing message, it continuesto receive the hailing message even after T1 seconds elapses. If thehailing message is acceptable, as will be discussed below, the PCDtransmits 70 a response, resulting in the initiation of a communicationsession.

As shown in row (C) of FIG. 4, the PCD 20 may attempt to receive 52"while the personal computer 40 is attempting to receive 72 a response.When the next hailing message 66 begins at time 68, the PCD detects it.If the hailing message is acceptable, the PCD transmits 74 a response,resulting in the initiation of a communication session.

The flowchart of FIG. 5 shows the logic performed by the PCD 20 and thepersonal computer 40 in establishing a communication session using theirrespective IR transceivers 32, 42.

As a first step 102, the PCD attempts to receive a hailing message. Ifthe PCD 20 is not within range, or within line-of-sight, of thecomputer's IR transceiver 40, then the PCD would not receive a hailingmessage, and the second step 104 would result in a negative answer. ThePCD would then wait for ten seconds, as shown by block 100 before againattempting to receive a hailing message.

After receiving a hailing message, the PCD 20 compares the received IDcontained in the hailing message with its internal security list ofacceptable IDs. If the ID is acceptable, as determined by step 106, thePCD transmits its ID in response, as step 108.

As next steps 110 and 112, the PCD 20 receives information from thepersonal computer 40 and transmits information to the personal computer.The information exchanged is discussed in more detail below.

The PCD 20 determines whether the communication session has beensuccessful in step 114, and if not, waits ten seconds before attemptingto receive another hailing message.

If the communication session is successful, the PCD 20 reconciles, asstep 116, the newly received information with the information it hadbefore the communication session. This reconciliation step is discussedin more detail below.

As a final step 118, the PCD 20 empties its "mailbox." The PCD keepstrack of the information to be sent to the computer 40. These can bedone by storing files to be sent in an "outbox" area of memory such asRAM 30, storing pointers to files to be sent, or simply attaching flagsto files to be sent. Whatever method is used for determining which filesneed to be sent, this final step 118 marks the files as no longerneeding to be sent.

The steps performed by the personal computer 40 in establishing an IRcommunication session are quite similar to those discussed above asbeing performed by the PCD 20. As a first step 130, the personalcomputer transmits a hailing message containing its ID.

The personal computer 40 then attempts to receive a response to itshailing message as step 132.

If a response is received, as determined in step 134, its ID is comparedwith the computer's internal security list as step 136. A negativeresponse to either of steps 134 or 136 results in the personal computer40 returning to the step 130 of transmitting its hailing message.

As next steps 138, 140, the personal computer 40 exchanges informationwith the PCD 20. The personal computer would transmit any information tothe PCD that was in its mailbox to be sent.

The personal computer 40 determines whether the communication sessionhas been successful in step 142, and if not, returns to the step 130 oftransmitting its hailing message.

If the communication session is successful, the personal computerreconciles the information it received in the session with theinformation it had before the session began, as step 144.

As step 146, the personal computer 40 empties its mailbox. The computerneed not use the same method of keeping track of which messages need tobe transmitted. Regardless of what method the personal computer uses, inthis step, it marks the transmitted information as no longer needing tobe transmitted.

The PCD 20 and personal computer 40 can exchange a broad variety ofinformation.

One type of information is scheduling information. The PCD 20 is anideal device for storing a day's scheduling information since it likelyto be worn while other electronic personal information managers,computers, or pager schedulers are left behind.

A user may enter scheduling information into the PCD using its buttons26, changed the scheduling information, or received new schedulinginformation over its paging receiver 34. A scheduling and diaryapplication on the personal computer 40 must be updated to remainaccurate.

Similarly, the user may have entered new scheduling information on thescheduling application on the personal computer, changed schedulinginformation, or received new scheduling information from another sourcesuch as a network, modem, or wireless receiver. The schedulinginformation on the PCD 20 must be updated to ensure its user has the newor changed information.

The PCD 20 can also send to the personal computer 40 any information itreceives by its paging receiver 34 from a paging network service.Weather forecasts, sports scores, winning lottery numbers, and stockinformation are all examples of information that can be received from apaging network service. A user may want these to be transmitted to thepersonal computer for storage or further analysis.

The personal computer 40 may receive information that the user may wanttransmitted to the PCD 20. The personal computer may receive informationfrom a network, paging service, or other information source. Thisinformation could be of the same types as the PCD receives from a pagingnetwork service discussed above.

The personal computer 40 also may receive electronic mail that the userwould like transmitted to the PCD 20 so that it may be viewed later.

Additionally, the PCD 20 and the personal computer 40 may exchange "timeof day" information. The PCD and personal computer both include internalreal-time clocks. For example, the time on the PCD could have been setmanually by the user, or could be updated many times each day by apaging network service. Likewise, the computer's internal clock couldhave been manually set by the user, or may be automatically updated by acentralized program on a network.

Each of these sources of time has associated with it a different degreeof accuracy. A manual setting of the time has a low degree of accuracy,probably not being more accurate than within a minute or two. Incontrast, a paging network service could provide a highly accurate time,such as could be provided by basing it on a standards clock.

The internal clocks of the PCD 20 and personal computer 40 also haverespective degrees of accuracy in maintaining time. Thus, the longer aclock has gone since being reset, the more effect its own lack ofaccuracy would degrade the accuracy of the time it maintains.

Preferably, the time of day information exchanged by the PCD 20 and thepersonal computer 40 would include the time and a number signifying itsdegree of accuracy. This number would account for the degrees ofaccuracy in the method of setting, the maintenance of time, and theamount of time that has passed since the clock was last set. The numbermay be expressed as a single byte, resulting in 256 potential degrees ofaccuracy.

In addition to the types of information discussed above, the PCD 20 andpersonal computer 40 may exchange other types of information. They mayexchange text files containing memos, project information, and news, aswell as graphics files containing information such as business chartsand weather maps. The PCD 20 need not be able to display the informationfor the PCD and personal computer to be able to exchange it. As isdiscussed below, the PCD may serve as an intermediate storage device fortransferring information between a user's work computer and homecomputer.

As part of the process of establishing and conducting a communicationsession, the PCD 20 and personal computer 40 reconcile the informationthey receive from the other with the information they already had beforethe communication session began. In reconciling the exchanged time ofday information, the personal computer 40 and the PCD preferably use thedegree of accuracy information to select whether to reset their internalclocks to match the time of day received from the other. If the time ofday received in the communication session has a higher degree ofaccuracy than its internal real-time clock 22, then the PCD 20 wouldupdate its clock to match the received time.

Scheduling information received in a communication session also can bereconciled automatically; the most recently changed information hasprecedence over previously entered or changed information. Although lessconvenient for the user, manual reconciliation, where the PCD 20 andpersonal computer 40 prompt the user to verify any reconciliationdecision, would ensure that the correct information remains.

The reconciliation of other types of information can be performed in thesame ways as for scheduling information, both automatically or manually.

After establishing and completing a communication session, the PCD 20and the personal computer 40 can handle subsequent communicationsessions in various alternative manners.

The PCD 20 could continue to establish communication session every 10seconds for as long as it is within range of the personal computer's IRtransceiver 42. Since the subsequent communication sessions presumablywould involve the transfer of less information, the subsequentcommunication sessions would be shorter and use less of the PCD'sbattery power. However, there is a baseline amount of power consumed percommunication session since certain amounts of information, such as theID and time of day information are transmitted by the PCD in eachsession.

Alternatively, the PCD 20 can ignore hailing messages that match ID ofthe personal computer 40 with which the PCD has recently had acommunication session. This ignoring mode can continue for a presettime, such as ten minutes, after which the PCD would respond to anyhailing message containing IDs in its internal security list. Ignoringhailing messages assumes that there is no new information of any importto exchange in the ignoring time period.

The PCD 20 can ignore hailing messages until an event occurs. One suchevent could be that the PCD fails to receive a hailing message from thepersonal computer 40 during one of the PCD's regular attempts toreceive. This could indicate that the user had left his office and thuscould have missed a message on his computer 40.

Also, the PCD 20 can ignore the personal computer's hailing messageuntil a hailing message contains a code signifying that the personalcomputer 40 has new information to transmit. Depending on the desiredsize of the ID, the hailing message may have additional bits left to useas a "new information" flag for this purpose.

Communication between a PCD 20 and a personal computer 40 has beendescribed primarily with reference to matching a single PCD 20 with asingle computer 20. That is, a PCD would communication with only asingle computer and a computer would communicate with only a single PCD.

This need not be the case. A PCD 20 could communicate with multiplecomputers 40. For example, a user may have a personal computer 40 atwork and another personal computer at home, but desires the PCD tocommunicate with both. By programming the IDs of both personal computersinto the security list of the PCD, the PCD can establish communicationsessions with both computers.

Similarly, a family may own a single personal computer 40, but have morethan one PCD 20. By programming the IDs of all the PCDs into thepersonal computer's internal security list, the computer can establishcommunication sessions with all of the PCDs.

Additionally, as shown in FIG. 6, a corporation may have multiplecomputers 40, 41a-41c on a network 156 with multiple users. A userhaving a PCD 20 could establish a communication session with anycomputer having the PCD's ID in its security list. In this manner,information intended for a user is more likely to be received if anycomputer on the network can transfer it to his PCD than if the user canonly receive the information from the personal computer 40 in his ownoffice.

To increase the capacity of an internal security list, entries in thelist may contain "wildcards." That is, a received ID need not have eachof its digits match a respective digit in the security list. Anexemplary format of a security IDs could define the first l digits asgeographical identification, the next m digits as companyidentification, the next n digits as division identification, and thenext o digits as personal identification. In such a case, a company mayprogram the security lists on its computers to accept as valid IDs anyID that matches at least the company and division information,regardless of the information in the other digits.

Referring again to FIG. 6, a PCD 20 may communicate with multiplecomputers 40, 41a-41c connected to each other by a network 156. Each ofthe computers has a respective IR transceiver 42, 43a-43c and telephone150, 152a-152c associated with it. The telephones are connected to eachother and to a telephone switch 154 by a telephone network 158. Thetelephone switch is also connected to the computer network 156 forreceiving commands therefrom.

The computers 40, 41a-41c preferably transfer electronic mail betweenthemselves and run a network-based scheduling application program.

According to another aspect of the present invention, at least one ofthe computers 40, 41a-41c monitors all attempted and establishedcommunication sessions between the computers and PCDs, only one of whichis shown by reference number 20. When one of the computers establishes acommunication session with a PCD, the user of that PCD is assumed to benear that computer. By sending a message to the telephone switch 154,the computers can command the switch to send all phone calls intendedfor the user's telephone to be rerouted to the computer that has mostrecently established a communication session with his PCD.

For example, suppose the user of PCD 20 enters the office containingcomputer 41b and telephone 152b. The user's office is the one thatcontains telephone 150. When the user's PCD 20 establishes acommunication session with the IR transceiver 43b associated with thepersonal computer 41b, the personal computer sends a command to thetelephone switch 154 to reroute all subsequent telephone calls intendedfor telephone 150 to telephone 152b.

It will be recognized that other systems could use information of thelocation of a wearer of a PCD 20. For example, the user could be givenaccess to certain programs and data on the computer 20 to meet softwarelicensing or data security requirements.

Referring now to FIG. 7, according to another aspect of the presentinvention, a PCD 20 may establish communication sessions with anotherPCD 170. For example, a PCD 20 can be programmed to contain an"electronic business card." The electronic business card is a file thatcontains the user's name, company name, address, telephone number,facsimile number, electronic mail address, and other such informationthat would commonly be found on a standard paper business card. Theelectronic business card can also contain more detailed information suchas past and current work projects.

To save battery life, a PCD 20 does not continuously attempting toestablish a communication session with another PCD 170. Therefore, tomanually exchange electronic business cards, two users of PCDs aim therespective IR transceivers 32, 172 of the two PCDs toward each other andpress a button 26 on the PCDs. The users need not press the buttonssimultaneously, and in fact cannot. However, this timing variance isused advantageously to establish a communication session.

Referring now to row (A) of FIG. 8, each PCD 20, 170, upon having thebutton 26 pressed goes initially into a receive mode 180, and then intotransmit hailing message mode. If a communication session is notestablished during the first cycle, the PCD attempts to receive for arandom period of time 180' and then transmits its hailing message again182'.

Refer now to rows (B) and (C) of FIG. 8 which show the establishment ofa communication session when both buttons are not pressed 26 at the sametime. The button on the first PCD 26 is pressed first, causing it to gointo receive mode 184 and then into transmit mode 186. At time 188, thebutton 26 on the second PCD 170 is pressed, causing it to go intoreceive mode 190. At time 192, the second PCD 170 begins receiving thehailing message 194 from the first PCD 20. After receiving the hailingmessage, the second PCD transmits 196 its ID in response, therebyestablishing a communication session between the two PCDs in which theyexchange their electronic business card information.

Refer now to rows (D) and (E) of FIG. 8. As before, the button 26 on thefirst PCD 20 is pressed first, causing it to go into receive mode 198and then into transmit mode 200. At time 202, the button 26 on thesecond PCD 170 is pressed, causing it to go into receive mode 204. Thefirst PCD enters receive mode 205 before time 206, at which the secondPCD begins transmitting its hailing message 208. In response toreceiving the hailing message, the first PCD transmits its ID 210,thereby establishing a communication session. As above, the two PCDsexchange their electronic business card information.

Referring now to rows (F) and (G) of FIG. 8, if the two users press thebuttons 26 on the first and second PCDs 20, 170 virtuallysimultaneously, then the PCDs simultaneously attempt to receive 216 andthen attempt to transmit 218, preventing a communication session frombeing established. As discussed above, after attempting to receive andthen transmitting without establishing a communication session, each PCDagain attempts to receive 220 for a random amount of time, and thentransmit again. In the example shown in the drawings, the first PCD 20again begins transmitting 224 its hailing message at time 222. Inresponse to receiving the hailing message, the second PCD 170 transmits226 its ID, thereby establishing a communication session.

Optionally, the first attempt to receive 216 by the PCDs could be for arandom time period.

It is possible that a PCD 20 does not establish a communication sessionwith another PCD 170 because they are not within line of sight of eachother, or the button 26 was inadvertently pressed. If no communicationsession is established within a certain time period, for example, 15seconds, the PCD would inactivate its IR transceiver 32 and alerts theuser to the failure.

Refer now to FIG. 9, which shows a flow chart of the manual electronicbusiness card exchange process. When the button 26 is pressed 230, thePCD 20 attempts to receive the other PCD's hailing message, as shown byblock 232. If the hailing message is received, as shown by block 234,then the PCD transmits 250 a response ID, receives 252 the electronicbusiness card from the other PCD 170, and then transmits 254 itselectronic business card.

Should the PCD 20 not detect a hailing message in its first attempt, ittransmits 238 its own hailing message, and attempts to receive 240 aresponse. If a response is detected, as determined by block 242, thenthe PCD 20 transmits 246 its electronic business card and then receives248 the electronic business card from the other PCD 170.

If a response to its hailing message is not detected, as determined inblock 242, then the PCD 20 again attempts to receive the other PCD'shailing message at block 232. This time, however, the PCD attempts toreceive the hailing message for a random amount of time.

Periodically, the PCD 20 determines how much time has elapsed in tryingto establish a communication session, as shown by block 236. Should theelapsed time exceed a preset period, then the PCD 20 alerts the user tothe failure, as shown by block 244, and quits trying.

The logic shown in FIG. 9 depicts the PCDs 20, 170 attempting to receivea hailing message 232 before transmitting their own respective hailingmessages 238. Although this is preferred, it is possible to reverse theorder and still establish a communication session. Likewise, either PCDcould transmit its electronic business card information first, notnecessarily in the order shown. Also, the check on elapsed time shown byblock 236 could occur elsewhere in the procedure, as long as the checkis regularly performed.

The PCDs 20, 170 can-use the ID information contained in the receivedhailing message to determine what electronic business card informationto send. For example, if the second PCD 170 has an ID that indicates itsuser works for the same company, the first PCD 20 could include companyconfidential information in the business card. As another example, ifthe other PCD has an ID that indicates it user lives in the samegeographic area, the PCD could include a weather forecast received froma paging network service.

If there is no match in IDs, then only a minimal amount of information,such as is typically found on a paper business card, is sent.

There are circumstances where users of PCDs 20 may want to automaticallyestablish communication sessions with personal computers 40, laptopcomputers, palmtop computers, or other PCDs. In this discussion, PCDsand the previously mentioned computers will be referred to as "devices."

Again, battery life considerations prevent PCDs 20 from continuouslyactivating their infrared transceivers in an attempt to establishcommunication sessions. Additionally, if two devices were tocontinuously communicate, they would prevent other PCDs within rangefrom being able to communicate.

Therefore, according to another aspect of the present invention, devicesuse time division multiplexing to divide the available time intomultiple time slots. The period of a time slot is long enough to allow areasonable amount of data to be transmitted within it. The number oftime slots is limited so that the slots recur within a reasonable time,such as ten seconds.

The chart of FIG. 10 shows a simple time division multiplex schemehaving n slots 260, where each slot has a duration of t seconds. Eachslot recurs in T=n·t seconds.

Within each slot 270, as shown by FIG. 11, are multiple transmit starttimes 272, allowing for multiple devices to communicate within the sameslot.

According to another aspect of the present invention, the time slot usedby a person, family, or work group is determined by a hash operation onthe name of the person, family, or workgroup desiring to communicate.This "group name" is programmed by the user into a "group list."

For example, a user may program the group name "Smith" into the grouplist of his PCD. The PCD performs a hash operation on "Smith" resultingin slot number to use for group communications. The same user canprogram the group name "Smith" into the group list of his othercomputers, and they all result in the same slot number for their groupcommunications.

If a hash operation results in a slot already in use by anotherindividual or group, a user can avoid the slot in use by changing thespelling of his selected group name, for example to "Smith1," or useanother arbitrary designation for the slot.

The transmit start position 272 of each device within a group ispreferably assigned according to a device number. Thus, if user Smithhas a PCD 20, a palmtop computer, and a desktop computer 40 that hewishes to all communicate on the same slot, he may arbitrarily assigndevice numbers 1, 2, and 3, to the devices, respectively.

In operation, a device looks to its "group list" to determine which timeslot to use. The device also looks to its device number to determine itstransmit start time within the time slot.

During the time slot, the device attempts to receive from other deviceswithin the same group. At its transmit start time within the time slot,the device attempts to start a communication session by transmitting itshailing message.

In a preferred embodiment, the hailing message would include the groupname contained in the group list. It could also include the number ofthe time slot. The transmission of the slot number allows for errordetection. Other, potentially unsynchronized devices may be withinreception range. It they receive a hailing message, they can detect theunsynchronized situation by comparing the received slot number with theslot number the device thought it was receiving.

If a device detects a hailing message within its time period, it sends aresponse. The two devices then establish a communication session thatoccurs within the current and subsequent occurrences of the time slot.

For time division multiplexing to work, all participating devices mustbe synchronized. That is, all devices must have each slot start at thesame time.

This can be accomplished by having each device know the exact absolutetime. Then, according to a predetermined formula, each device candetermine the starting time of each time slot.

For example, if time slots repeat every 30 seconds, a convenient formulawould be to have time slot 1 start at each minute and at eachhalf-minute. All other time slots could then be calculated by theirrespective numbers and the period of each slot.

Synchronization can also be accomplished by having each device know onlythe exact relative time. That is, a device need not know the time of dayto know that slot 1 is starting. It need only be told when slot 1 startsonce, and then can keep track of the current time slot from that timeforward.

In other words, knowledge of the absolute time is not necessary, butknowledge of the absolute time modulo the repeat period T is.

According to another aspect of the present invention, a PCD 20 may besued to send information between two computers. As discussed above, auser may have access to at least two computers, for example, having onecomputer at work and another at home. There are circumstances when sucha user would like to be able to transfer information between thecomputers. This may be accomplished by having the first computertransmit the information to the PCD 20. Then, when the user is at thesecond computer, the PCD transmits the information to it.

Referring now to FIG. 12, a personal computer 40 having an IRtransceiver 42 can establish an IR communication session with a PCD 20via its IR transceiver 32. If the PCD has a wireless radio-frequencyreceiver such as a paging receiver 34 (FIG. 1), the computer can alsocommunicate with the PCD by calling the paging service's computers 282using a modem 278 via the public telephone switch 280. The pagingservice's computer transmits the message to the PCD using it broadcastfacilities 284.

According to another aspect of the present invention, a portablecommunication device 20 that has dual communication links allows acomputer 40 that receives a message for the portable communicationdevice's user to choose which communication link to use to send themessage.

Referring now to FIG. 13, a personal computer 40 receives a message forthe user of a portable communication device 20, as a first step 290. Anexemplary message would be an electronic mail message indicating ascheduled meeting received from another computer by way of a network. Asa second step 292, the personal computer 40 determines the due date ofthe message. If the due date is less than a predetermined time periodaway, then as a third step 296, the computer sends the message to thePCD by sending a message to the paging service's computers 282 which, inresponse, transmits the message to the PCD 20 via the broadcastingfacilities 284. However, if the due date is greater than thepredetermined time period away, then as an alternative third step 294,the personal computer 40 places the message in its outbox to betransmitted to the PCD 20 in the next infrared communication session.The predetermined time period could be set by the user to reflect howoften the user was likely to be near his desktop computer 40.

It will be recognized that this need not be limited to infrared andradio-frequency transmissions. This method may be used advantageouslywith other pairs of communication channels.

The terms and expressions that have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized the scope of theinvention is defined and limited only by the claims that follow.

I claim:
 1. A system comprising in combination:a terminal whichbroadcast hailing messages, said hailing messages being broadcastrepeatedly at a first periodic rate utilizing electromagnetic radiationhaving a wave length shorter than radio waves, and a receiver comprisinga periodically operative, wrist mounted, battery operated device, saidreceiver having a wristwatch form factor and an identification number,said receiver having means for receiving said hailing messages and meansfor transmitting to said terminal said identification number in responseto the receipt of a hailing message, said means for transmittingutilizing electromagnetic energy having a wave length shorter than radiowaves for said transmission, said terminal including means for storingmessages addressed to said receiver, and means for transmitting saidmessages to said receiver in response to the receipt of saididentification number.
 2. A system including in combination:a computerhaving stored therein messages, each of said messages addressed to aparticular identification number, said computer including first meansfor periodically transmitting hailing messages utilizing electromagneticenergy having a wave length shorter than radio waves, said hailingmessages being transmitted at a first periodic rate, a wristwatch havinga first identification number, first receiving means in said wristwatchfor receiving said hailing messages transmitting means in saidwristwatch for transmitting to said first means said firstidentification number, second receiving means in said computer forreceiving said identification number and for transmitting to said firstreceiving means messages addressed to said first identification number.